Worms (Horsehair worms) Gordius species

Horsehair worms of the phylum Nematomorpha are parasitoid animals whose larvae are parasitic on terrestrial arthropods, such as beetles, wetas, cockroaches, crickets and millipedes. They range in size from 50 to extreme cases up to 2 metres and are 1 to 3 millimetres in diameter. The adult worms are free-living in damp areas and can be found in fresh shallow water areas like ponds, troughs and swamps.

A conservative estimate suggests that there may be about 2000 freshwater species worldwide.The adult worms possess an external cuticle without cilia. Internally, they have only longitudinal muscle, a non-functional gut and sexual organs. They have no excretory, respiratory or circulatory systems.Reproductively, they are dioecious, with the internal fertilisation of eggs that are then laid in gelatinous strings. It depends on water temperature when the eggs hatch. It can vary from 2 to 12 weeks.The tiny larvae live in the water after hatching and are ingested with water when insects drink. Once inside a host insect, the larva penetrates the insect’s gut and enters its body cavity. Here they digest and absorbs the surrounding tissue. In two to three months when they become adults they escape from the host by boring through the insect’s exoskeleton. It is interesting that the mature worms affect the brains of the hosts, forcing them to enter the water where the worm emerges for the aquatic breeding stage.

It is presumed that they are harmless to humans.

A photo of a 34 cm long.adult horsehair worm of the Gordius species found in the Pureora Forest Park.

Photo of the same worm as in the above photo.A muddy rain filled pool on a track in the Pureora Forest Park that was infested with horsetail worms.